Peptide-Based Systems for the Targeted Disruption and Treatment of Staphylococcus epidermidis Biofilms

Complications due to nosocomial infections of implanted medical devices pose a significant health risk to patients, with Staphylococcus epidermidis often implicated in the case of blood-contacting biomaterials. One method by which S. epidermidis initially adheres to biomaterials uses the plasma protein fibrinogen as an intermediary, where the S. epidermidis surface protein SdrG binds to a short amino acid sequence near the amino terminus of the Bβ chain of fibrinogen. This study reports on the use of this fibrinogen-derived β6-20 peptide for the targeted disruption of S. epidermidis biofilm formation using a cationic peptide, as well as the specific delivery of vancomycin to S. epidermidis biofilms.

S. epidermidis virulence relies mainly upon its ability to form a biofilm, the main component of which is polysaccharide intercellular adhesin (PIA). The synthetic β6-20 peptide was utilized to deliver a cationic polylysine peptide (G₃K₆) to the bacterial surface and disrupt the charge-charge interactions needed for PIA retention and biofilm stability. The effects of the β6-20-G₃K₆ peptide on biofilm formation were assessed using optical density, fluorescently labeled wheat germ agglutinin, nucleic acid stain (SYTO 9), and a metabolic assay (XTT, 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt). Biofilms formed in the presence of β6-20-G₃K₆ peptide (100 μM) resulted in a 37.9% reduction in PIA content and a 17.5% reduction of adherent bacteria relative to biofilms grown in the absence of peptide. These studies demonstrate the targeting ability of the β6-20 peptide towards biomaterial-adherent S. epidermidis, and highlight the potential for disrupting the early stages of biofilm formation.

Targeted β6-20-PEG_x-VAN vancomycin derivatives were then synthesized using a flexible, variable length poly(ethylene glycol) linker between the peptide and antibiotic. Initial binding to surface adherent S. epidermidis was increased in a concentration-dependent manner relative to vancomycin for all equivalent concentrations ≥4 μg/ml, with targeted vancomycin content up to 22.9 times that of vancomycin alone. Retention of the targeted antibiotics was measured after an additional 24 hour incubation period, revealing levels 1.3 times that of vancomycin. The results demonstrate the improved targeting and retention of vancomycin within a biofilm due to the incorporation of a specific targeting motif.